1 1/2 teaspoons salt, divided

1 teaspoon ground cumin

3/4 teaspoon freshly ground black pepper

1/2 teaspoon smoked paprika

6 garlic cloves, minced

3 tablespoons canola oil, divided

1 (4 1/2-pound) flat-cut brisket roast (untrimmed)

4 cups unsalted beef stock (such as Swanson)

1 (12-ounce) beer

3 medium onions, sliced

3 tablespoons cider vinegar

2 tablespoons brown sugar

1 1/2 teaspoons cornstarch

1 1/2 tablespoons chopped fresh thyme